The present disclosure relates in general to semiconductor manufacturing technology, and more particularly, to inspecting defects on semiconductor wafers associated with photomask precipitates.
Photomasks (sometimes called reticles) are commonly used for photolithography in semiconductor manufacturing. Photomasks are typically made from very flat pieces of quartz or glass with a layer of patterned material (e.g., chromium) deposited on a side. The patterned material is used to transfer an image to a substrate such as a semiconductor wafer. The patterned material can be selected or arranged to form a BIM (Binary Mask), a PSM (Phase Shift Mask), or combinations thereof, to effectively pattern a projected amount of radiation being exposed during photolithography. While contamination of photomasks has always been a problem, high precision masks, such as are used in photolithography having wavelengths equal to or less than 248 nm, are particularly susceptible to defects. One type of photomask contamination is referred to as haze contamination. Haze contamination is a precipitant formed from mask cleaning chemical residual or impurity of fab or tool environment cross exposure. For example, when a solution including ammonium (NH4) and sulfate (SO4) is used to clean a photomask, contamination becomes apparent when the photomask is exposed to a short wavelength UV light, such as 248 or 193 nm. However, periodically inspecting or re-qualifying photomasks is costly and time consuming.
Therefore, what is needed is a simple and cost-effective method and system for inspecting semiconductor wafers to classify defects on a photomask.